1. Field of the Invention
The present invention relates to an imaging device, a focusing control method, and a computer readable medium storing a focusing control program.
2. Description of the Related Art
In recent years, with an increase in resolution of imaging elements, such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor, there has been a rapid increase in demand for information devices having an imaging function, such as a digital still camera, a digital video camera, and a smartphone. The information devices having an imaging function described above are referred to as imaging devices.
In these imaging devices, as a focusing control method which focuses on a main subject, a contrast auto focus (AF) method or a phase difference AF method is employed.
The contrast AF method is a method which calculates evaluation values of sharpness from captured image signals acquired in movement positions of a focus lens while moving the focus lens in an optical axis direction and determines a lens position having a highest evaluation value as a target position of the focus lens.
JP1995-7650A (JP-H7-7650A) describes an imaging device that performs focusing control through the contrast AF method.
In a case where the focus lens is moved in order to acquire the evaluation values, the imaging device performs acceleration and deceleration control such that the focus lens is moved at a high speed for a period during which a change in evaluation value is small and the focus lens is moved at a low speed for a period during which a change in focusing evaluation value is large. According to the acceleration and deceleration control, it is possible to increase the speed of the focusing control while securing focusing accuracy.
JP1989-239514A (JP-H1-239514A) describes a system that controls a movement speed of a focus lens in a case where the focus lens is moved in order to search for a target position based on information stored in an imaging device and information stored in a lens device attached to the imaging device.
JP2007-299997A describes an imaging device that controls a movement range of a focus lens in a case where the focus lens is moved in order to search for a target position.